Thermostatic switch



NOV 25, 1952 L.. H. WALBRIDGE THERMOSTATIC SWITCH 2 SHEETS--SHEET lFiled Dec. 30, 1948 wn m9 mm. mh

Iawno Lywa/ITI. Wa

Patented Nov. 25, 1952 rHERi/ios'mric swircn Lyman H. `l/Valbridge,Ashland, Mass., assignor to Fenwal Incorporated, Ashland, Mass., acorporation of Massachusetts Application December 30, 1948, Serial No.68,126

(Cl. 20D- 137) 4 Claims.

This invention relates to thermostatic switches, particularly those ofthe bowed-strut type as manufactured by Fenwal Incorporated of Ashland,Massachusetts, and as represented for example by the devices of U. S.Patents Nos. 2,090,407, 2,185,433 and 2,257,990. An important object ofthe invention is to minimize objectionable effects of occasionalexcessive temperature conditions. This is accomplished under theinvention by aiording the switches capacity to overshoot in the event ofabnormal temperature rises. The invention provides an over-travelcapacity for the stated type of Vcontact-carrying switch element,applicable in association with various forms of thermo-responsiveactuator other than as illustrated in said patents including an externalrod and tube type and others. Other objects and advantages will beapparent from the following description in connection with the drawingsexemplifying certain embodiments of the invention, and wherein:

Fig. 1 is a longitudinal sectional View of an inbowed-strut form of theswitch, for cool closure and for opening on heating to a set point;

Fig. 2 is a similar longitudinal section of an inverse or outbowed-strutform of the switch, to be open when cool and to close at the selectedhigher temperature;

Figs. 1A and 2A are cross-sections on the lines IA-IA and 2A-2A of Figs.1 and 2 respectively;

Figs. 3, 4 and 5 are partial longitudinal sections showing the Fig. lform of the switch in different operative positions: 'in Fig. 3 thetcmperature is assumed to be below the set point, the contactsaccordingly being closed; in Fig. 4 the assumed temperature is at ornormally above the set point and the contacts have opened; while Fig. 5illustrates the switch as when subject to excessive temperature,'abnormally above the critical temperature setting, the contactsremaining open; and

Figs. :6, '7 and '8 illustrate an inverse switch such as that of Fig. 2under similar temperature conditions as stated for Figs. 3, 4 and 5respectively.

Referring to the drawings in more particular and lirs't to Figs. l and 3to -5 lthe switch as a whole comprises a tubular case or shell i cimetal or other ymaterial of appropriate strength and rigidity and havinga relatively high cocincient oi expansion, that is, distinctly greaterthan that of the circuit-controlling element to be described. Sui-tablematerials include brass and stainless steel. The circuit-controllingelement `or switch unit designated generally at 20 is operativelydisposed within the case I6. it includes oppositely bowed metallic leafsprings 2 i, 2l composed of a metal having a relatively low thermalexpansion coeiiicient, such as Invar, or a similar nickel-iron alloy,tungsten, etc. In the Fig. l embodiment the spring members 2i are bowedinwardly as preferred for the regularH form of this type of switch, forcircuit closure when cool or at relatively low temperatures, breaking outemperature increase to a set point.

'Ir'he case lil is closed at its opposite ends by wall means on andbetween which the circuit controlling element 2i) is mounted. At theouter or supporting and adjusting end the case it has fixed to it a heador cap I I with an opening i2 for the insulated electric conductor-s i3sealed therein as at i4. The head ll may be variously constructed andarranged, according to the manner of mounting of the switch, conveniencein the location oi the conductor entrance, and other factors dependenton particular use requirements, the mounting flange I5 and lateralconductor passage as herein shown being merely illustrative.

The opposite or inner end of the switch case is closed by a rigid wall,herein a plug or disk i6 having threaded or other firm seatingengagement with the case iii, the terminal edge of which may beinturned. This end wall or disk IS carries centrally of the innerportion a rigid post or abutment il formed for thrust engagement withthe adjacent end of the switch unit 20 in spaced relation to the caseend wall i5.

Each spring member V2i of the switch unit 20 has an electric Contact,button or point l2v2 fixed at the central portion as by means of a metalclip 23 surrounding the respective spring and insulated from it by anonconductive wrap of mica, synthetic sheet material, libre glass or thelike 2d. The terminals of the insulated conductors IS are soldered orotherwise electrically connected to the respective contact clips 23.

The circuit-controlling switch unit 20 has at each end a supporting head25 and 35. The head 25 toward the mounting end of the switch coinprisesa tubular body or sleeve 215 with a medial iiange 21 which is recessedat opposite sides to receive the spring members 2l, il laterally. Theends of the latter are inturned and apertured to lit the sleeve, so asto be clamped between the medial flange 2l and a washer-'like disk heldon the sleeve as by an overset shoulder or end Iiange 25a thereon.

The described head 25 is installed on and made rigid with the inner endof an elongated anchor stud 2S. This stud has an extensive threadedportion received in the like-threaded axial bore of an adjusting sleeve30 for regulating the temperature set-point for the switch. Thisadjusting sleeve 35 in turn has external threaded engagement in athrough opening in the end wall of the switch head l I. The insulatedconductors I3 may be given one or more turns within the case, hereinaround a protective tubular positioner 3l extending inwardly from theswitch head l I, surrounding and spaced from the anchor stud 2S and theadjustable setting sleeve 35.

At the opposite or inner end of the circuitcontrolling element thesupporting head 35 comprises a body 36 having medial flange 3'! and anouter shoulder or end flange 38. The adjacent inturned and apertured orrecessed ends of the contact-carrying springs 2l are at this end of theunit received and held between the medial iange 3l of the head 35 and awasher or disk 39 abutting the end ange 33.

The outer end portion of this supporting head 35 of the switch unit isformed with a central cavity or bore i0 adapted to receive loosely theinner portion of the post or abutment l' previously mentioned. The freeend of the post Il and the end wall of the bore #l0 of the head 35preferably are mutually shaped in a concavo convex relationsubstantially as shown to provide for self-centering and self-aligningthrust bearing engagement with each other. The depth of the bore 150 andlength of the post l1 are proportioned to afford capacity for relativebodily movement axially between them over an appreciable distance whileretaining relative axial guided alignment. The head 35 and post il thusconstitute an automatically aligning bearing and abutment couple, withcapacity for relative separation in the direction axial of the case i9.

The head 35 and the switch unit 25 as a whole when assembled in the casel0 are held against relative turning, without interference with thecapacity for relative longitudinal expansion and contraction. Suitablemeans for the purpose may be for example as in Patent 2,257,990previously mentioned, including one or more internal ribs Ilia on thecase I slidably received by corresponding notches 21a in the main flange2 of the head 25; see particularly Fig. la, also Fig. 2a

with reference to the embodiment of Figs. 2 and Referring now to theouter or mounting end of the switch, at the right in the views, thedescribed stud 29 and sleeve 30 in cooperation with the case head Il andassociated parts to be described provide for adjusting the switch to andsecuring it at the selected temperature setting. Similarly as in saidPatent 2,257,990 the threading of the stud 29 and the internal threadingof the sleeve are of different pitch than the external threading of thesleeve and of the case head H which receives the latter. Turning of theadjusting sleeve 30 in one or the opposite direction consequently bodilyshifts the stud 29 lengthwise in or out. This accordingly increases ordecreases the extent of longitudinal expansion of the case I9 requisitefor actuation of the relatively non-expanding leaf springs 2 l.

Herein novel provision desirably is included for insuring retention ofthe adjustment at the selected set point, against unintended alteration.Accordingly the adjusting element or sleeve Sil has threaded on it atransversely slotted collar 50 having ears 52, 53 in alignment on therespective divided portions. A lock screw 54 is threaded through alignedthreaded apertures in the ears 52, 53. A non-threaded extension 55 ofthe lock: screw 55 projects into a recess 56 for the pure pose in thecase head Il. Turning of the screw 55 in one direction biases the ears52, 53 toward each other, causing the collar to grip and hold"A thesleeve 30 in any set position and against un intended relative turningof the latter. Unison'. turning of the sleeve 30 and the collar 5] isposi-- tively prevented by the extension of the lock. screw 513 into thecase head li. When it is de sired to change the setting preliminaryrelease of the lock screw 54 permits the sleeve 39 to be turned in theappropriate direction to increase or to reduce the compression on theswitch unit 29.

The switch embodiment of Fig. 1 and Figs. 3 to 5 maintains circuitclosure when cool or comparatively so. Thus it is particularly adaptedfor applications where a circuit is to be broken in response totemperature rise, the switch setting being adjusted for opening of theswitch points 22 upon arrival of the particular critical temperatureconcerned. In the cool status, at temperatures below the set point, theswitch unit 20 is in some degree of longitudinal compression, beinginstalled and adjusted to a closing compression at average expectedambient temperatures, for example, room temperature. The describedadjustment to the desired set point for opening may be made initially orsubsequently at the place of use. This is accomplished by releasing thelock screw 515 and turning the sleeve 55 in the appropriate direction toincrease the compression upon the switch unit, as calibrated for theparticular switch.

One turn of the adjusting sleeve 35 may be equivalent, merely by way ofillustration, to say a F. shift of the set point. Merely to cite onespccic example, assuming a room or normal ambient temperature of say F.and a desired opening set point of 285 F. the setting is made such thata 210 rise above '75 F. with the attendant relative expansion of thecase l5 will result in switch opening. In other words, the adjustingsleeve 30 is turned in the appropriate direction and to the extent, e.g. three turns at the 70 per turn calibration of the above illustration,to place the switch unit 2i) under such longitudinal compression as willbe relieved to a switch-opening condition by that degree of diferentialexpansion of the case I0 and the switch unit 29 corresponding to a 210F. temperature rise. t will be understood that within the totalavailable range of the particular switch, opening set points forrelatively high temperatures require a greater longitudinal expansion ofthe case than those for lower temperatures.

Referring now more particularly to the somewhat diagrammatic Figs. 3 to5, corresponding tc Fig. 1, assume now that the switch has been adjustedto the desired set point for opening, such as at 285 F. of the previousexample, or it may be 300, 350, 400 or other selected point within thetotal operative range. Fig. 3 then represents the parts as in the normalor cool status. The switch unit 20 is under appropriate longitudinalcompression for the switch points 22 to be closed as there shown. At therighthand end of the unit 20 the compressive force is applied by thecase head H, the adjusting screw 30 and the anchor stud 2S to the switchunit head 25 rigid with the latter. Opposing these, at the other end ofthe switch, are case end wall I6 and the abutment post Il in directthrust-bearing engagement with the adjacent switch-unit vhead 35. Inthis embodiment the inherent tendency of the inbowed switch leaves 21,2l 'is to straighten, in the opening direction. They maybe assembledunder some initial coinpression or otherwise as preferred. Theccmpressive force as above referred to in yconnection with Fig. 3opposes the straightening effort and vholds the points 22 closed in thecool status.

Fig. 4 represents the same switch unit upon arrival of that temperatureto which the set point is adjusted. The switch case I9 has relativelyexpanded and lrelieved compression on the *unit 20 suiiciently to permitthe two inbowed members to straighten enough to separate the switchpoints 2v2, 22. The switch circuit accordingly is opened.

Still'referring to Fig. 4, itis here assumed -that the effectivetemperature has not excessively or abnormally exceeded -the set point.The compression of the unit 29 has been characteristically relieved,adequately for the opening action of the switch points. But thecompressive condition as -between the opposite ends of the switch isstill such that vthe abutment post il and the thrust bearing 3S of theswitch-unit head 35 remain in direct contact or substantially so. 'Thiscondition of longitudinal thrust engagement as between the abutment posti1 and the thrust bearing l36 of the switch-unit head 35 may prevailthrough any ordinarily expected rise in temperature above the set point,depending on the degree of compression under which the switch isinitially assembled.

However, operating conditions not infrequently are encountered whereinthe switch may be subjected to extreme temperature rises, of anexcessive and abnormal degree. Such emergency condition might beoccasioned by the failure of a cooling system in connection with someindustrial process, or by the failure of lubrication as for example inthe case of a hot-box at a railway car journal where the temperature maycontinue to rise greatly above the set point at which the switch opened,or by re or other emergencies. sive temperature conditions, permanentdistortion, rupture or other damage of the switch parts has heretoforeoccurred. This applies not only to devices of this type in which bothends of the switch unit are rigidly connected to the case,

as for example in Patent 2,090,407, but also those in which any capacityfor relative axial movement, other than dierential expansion, has beenavailable only in the axial direction inwardly as to the case andoutwardly as to the switch unit, as for example in Patent 2,257,990,wherein substantial undershooting of the temperature is ac commodated.

Again referring 'to Fig. 4, the switch-unit head 25 at the right isrigidly connected to the case through the post 29. lf now the other endor head 35 also were rigidly associated with the post Il' or otheradjacent part of the case is, or were such as to permit onlyiii-movement of the case end member as in Patent 2,257,990, thencontinued vexpansion of the case i@ in the Ipresence lof some excessivetemperature 'condition would tend to subject the switch-unit Eil todamaging tension. This is likely to cause brealage at the endconnections, or to deform the switch leaves, and to disturb theelectrical connections and particularly the adjustment of the set point.Hence on restoration of temperature conditions to within the normaloperating range the switch would function unreliably or is inoperative.

Under any such emergency excesa switch unit 200 Aof the inverse type.

sponse to temperature rise.

In accordance with the present invention ithe construction, arrangementand interconnection for the switch unit 20 and casing I0 as hereindisclosed and already herein described with reference to the drawingsare made such that excessive temperature rise to the abnormal extentconcerned, herein termed temperature overshooting, can occur not onlywithout damaging effect to the switch, but also without disturbing theselected temperature setting. The switch accordingly is afforded thecapacity to vwithstand such overshooting vand subsequently `to vresumenormal functioning automatically upon return of temperatures within theordinary operating range, without necessity for replacement of parts orreadjustment to the given set point.

Turning now to Fig. 5 and noting particularly the left end portion, theparts are illustrated `in an overshot or emergency excess temperaturecondition. The case |40 as shown has expanded to such abnormal extent asto carry the end wall i6 and abutment post l1 outwardly toward the leftcompletely out of end-thrusting Contact with the switch-unit head 25 andthe thrust bearing 36 thereof, to the extent as represented by thespacing 40 indicated on Fig. 5. There is no positive connection betweenthe head 35 and the lpost -II or other adjacent case part to inhibit theseparating action illustrated. The resultant capacity for free bodilyoutward movement of the abutment post Il accordingly leaves the switchunit 20 in a condition of `complete freedom from Ythe otherwiseresultant excessive tensioning Aand distortion. `Thus the severestresses and strains characteristic of overshooting are relieved fromthe switch unit, under the present invention. Further, by reason of thecoopera- -tive guiding, aligning and self-centering relation as betweenthe abutment post I1 and the thrust bearing 36 of the switch-unit head35 `subsequent decrease of the temperature to the normal rangeautomatically restores the parts for resumed normal operation andaccurately subject to the same opening set-point as previously. It willbe understood that in the somewhat diagrammatic views the spacingrelations as between the switch points 22 and alsoI as between theabutment II and switch-unit head 35 may be regarded as somewhatexaggerated, for clearness.

In Figs. 2 and 6 to 8 the invention is further illustrated as embodiedin a thermostat having There the switch Astruts or leaves -2i0 areoutbowed. The switch points 220 accordingly are open in the coolcondition and close to make circuit in re- The case i0, cap Il and partsassociated with the latter, including the anchor stud 29 and settingsleeve 3U may Yin general be as in the previous gures.

-At the right or supporting end the outbowed switch springs 2 l0 are'formed with semi-tubular extensions '2l l, similarly asin Patent2,185,433.

These receive the inner end of the stud 29 and are themselves enteredinto a head-piece 250 having a flange 25S. The stud 29, spring ends 2liand the head-piece 253 are rigidly secured together as by spot weldingor otherwise. As indicated in Fig. 2A, one or more internal projections10a on the wall of the case, similarly as in the .previous iigures,engage the flange 25| to prevent tortional rotative movement of theswitch unit 200 relative to the case l0. The contact .points 220, Vtheattaching clips 239 therefor and the insulation 240 forthe respectiveswitch leaves 210 may be as previously described.

At the opposite or inner end, toward the left in the views, the switchunit 200 has separable abutive engagement with the case l through theend wall I6 and the post or abutment Il thereon. In this instance theseparable connection aiording the overshoot capacity comprises acup-like thrust bearing or head 350 including a recessed body 36E)having at its inner end a central boss 36| slotted to receive the atwisejuxtaposed ends of the outbowed springs 2li). The spring ends are weldedor otherwise rigidly secured to the bearing head member 350. The centrallongitudinal bore 352 opening from the outer end face of the body 36! isdisposed in axial line with the attached springs EIB. It is adapted toreceive loosely the abutment Vpost il. The inner end wall of the bore362 and the free end of the post I7 again as in the previous embodimenthave a concave-convex relatio-n for mutual self-centering andself-aligning abuttive interengagement.

In operation the thermostatic switch of Figs. 2 and 6 to 8 functions ina reverse manner to that of Figs. l and 3 to 5, as regards circuitclosure. Due to the inverse or outbowed relation oi the contact-carryingspring pair 210, straightening tension thereon tends to close the points226. In the normal or cool status the switch is open, as in Fig. 2 andin Fig. 6; compare the latter with Fig. 3 of the earlier views. Thus theFig. 2 device is especially adapted for uses in which a circuit is to bemade or closed in response to temperature increase, examples of suchapplications being in the fields of refrigeration and airconditioning.

Fig. '7, comparing with Fig. 4, illustrates the ordinary functioning ofthe switch unit 201) on arrival of temperature equivalent to theselected set point or but normally above it. The switch points 220 cometogether and establish the circuit. 'Ihe thrust couple comprising theabutment post l1 and the switch-unit head 350 re- Y ditions suchemergency is taken care of with minimum danger of distortion of theparts or disturbance of the selected temperature setpoint. By reason ofthe guided self-aligning and self-centering bodily separable connectionsas between one end of the switch unit 2te and the case I6, the deviceautomatically accommodates itself to such overshooting of temperature atthe switch location. The resultant overshot condition of the parts isrepresented in Fig. 8 where the attendant spaced separation of the postIl and switch unit head 350 is indicated at Litt. There it will be notedthat the circuit remains closed, the reverse condition from that in theovershot status of the previous embodiment, Fi 5.

g'herrnostatic switches of the invention as herein disclosed, whether ofthe regular type of Fig. l primarily designed for contact breaking uponpre-set temperature increase or of the inverse type of Fig. 2 forcontact making in like event, may have a normal operating range of wideextent, as for example from -50 F. up to 400 F. or thereabouts; that is,the set-point for actuation may be at any temperature level selectedwithin such range. Yet the devices of the present invention are capableof overshooting so as to withstand abnormal excess emergencytemperatures as high as 1000 to 2000 F. or more, automatically resumingthe intended circuit control upon return to normal operatingtemperatures, the set-point adjustment and the intended operation beingin most instances unaffected by the precedent overshooting.

It has been pointed out earlier herein that the bowed or spring strutclement or switch unit may be installed under longitudinal compressionor otherwise and it is here noted that the installation may be such asto omit compression or even to place the strut end supports initiallyunder longitudinal tension. Thus it is apparent that as to either of theembodiments, whether the inbowed form of Figs. l and 3 to 5 wherein thespring bias of the struts is normally toward a separation of thecontacts or the out-bowed form of Figs. 2 and 6 to 8 wherein the naturalspring bias is toward closing of the contacts, the circuit-conditioningrelation of the contacts may be for any given initial or normaltemperature setting arranged as circuit-making or as circuitbreakingaccordingly as the switch unit or element is initially installed underlongitudinal compression or under longitudinal tension. Thus as toeither the regular type oi Figs. l and 3 to 5 or the inverse type oiFigs. 2 and 6 to 8, the directional sense or the circuit-conditioningrelation of the contacts may also be determined in accordance with thepresence or absence of initial longitudinal compression or the presenceor absence of initial longitudinal tension. 'Hence irrespective of thedirection o spring bias or bowing of the struts the switch of theinvention may be characterized as ci the compression or of the tensiontype. From this it will be further apparent that in certain embodimentsthe materials or metals of the shell and of the contact element orswitch unit may be selected to have substantially the saine andpreferably low properties of and capacity for thermal elongation andcontraction, the shift in the circuit-conditioning relation of thecontacts then being determined by variation in the eiiectivelongitudinal force, by way o1" augmenting or relieving the compressionor the tension as the case may be. rEhe provision for over-travel hereindisclosed as between the contact element or switch unit on the one handand the shell or the positioning connection between it and the adjacentend of the element or unit on the other hand is equally applicable inany instance, whether actuation results from differential expansion andcontraction as between the element and the shell or from variation cithe compression er the tension effective upon the element or by acombination of thermal and compression-tension variations.

It will be evident that the novel means hereindisclosed accommodatingthe thermostatic switch to overshooting may be incorporated at either'end of the switch units 2i) and 250, the same applying also to the meansfor adjusting the set point, and that said means need not necessarily beat the opposite ends or" the unit as shown herein by way of example andas preferred for ease in manufacture and assembly.

My invention is not limited to the particular embodiments thereofillustrated and described herein, and I set forth its scope in myfollowing claims.

I claim:

1. A thermostatic switch comprising an elongatedpase having a relativelyhigh expansion coefcient, a switch unit therein including a lon- 9gitudinal pair of oppositely bowed spring strips with a relatively lowexpansion coefficient, stripconnecting heads at the respective ends ofthe switch unit, a longitudinally adjustable stud extending into thecase at one end thereof, and supportive connections between the stud andthe adjacent switch-unit head and between the other case end and theswitch-unit head adjacent thereto, one of said connections comprisingseparable interfitted elongated post and cup abutment and bearingformations with terminal concavo-convex relative shaping forself-centering axial abutive thrusting engagement, release andreengagement providing for extension of the case independently of theswitch-unit under temperature overshoot.

2. A thermostatic switch comprising an elongated case having arelatively high expansion coeiicient, a switch uni-t therein including alongitudinal pair of oppositely bowed spring strips with a relativelylow expansion coeicient, strip-connecting heads at the respective endsof the switch unit, anchor means rigidly connecting one switchunit headand the adjacent end of the case, an abutment post xed on Iandprojecting inwardly at the other case end, and a post-receiving cuplikebearing formation on the corresponding switch-unit head, said post `andbearing formation dening a self-aligning axially separable thrust coupleof extensively overlapping axial reach and adapted rautomatically torelieve the switch from temperature overshoot effects.

3. A thermostatic switch comprising a case, a pair of oppositely bowedcontact-carrying spring strips longitudinally disposed in the case,strip connecting heads at each end of the pair, positioning connectionbetween the heads and the case portion respectively opposite each ofthem,

said connections for one head including a stud having an adjustingsleeve threaded thereon and extending out through the case in .threadedrelation thereto whereby turning of ythe sleeve axially shifts the studfor selecting the set-point for the switch, and locking means for theadjusting sleeve including a ltransversely divided lock collarexternally received on it, axially -aligned clampscrew receivingformations on the respective divided portions of the collar, :a clampscrew extending through said formations and a recess in the switch caseto receive the inward extending end of the screw.

4. A thermostatic switch comprising an elongated case having arelatively high expansion coefficient, a switch unit therein including alongitudinal pair of oppositely bowed spring strips with a relativelylow expansion coeicient, stripconnecting heads at the respective ends ofthe switch unit, a longitudinally adjustable stud extending into thecase at one end thereof, supportive connections between the stud :andthe adjacent switch-unit head and between the other case end and theswitch-unit head adjacent thereto, one of said connections comprisingseparable abutment -and bearing formations providing for extension oflthe case independently of the switch-unit under temperature overshoot,an adjusting sleeve threaded on the stud and itself threaded through thecase, a lock collar ythreaded externally onto the adjusting sleeve, andreleasable means for gripping the collar Iand sleeve against relativeturning and for positively engaging the case to prevent unison turningof the collar Aand sleeve relative thereto.

LYMAN H. WALBRIDGE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,791,477 Eaton Feb. 3, 19312,185,433 Fenn et al Jan. 2, 1940 2,257,990 Turenne Oct. 7, 19412,497,663 Eaton Feb. 14, 1950 2,559,372 Rike July 3, 1951

